MEMS (micro electromechanical systems), MOEMS (microoptoelectromechanical systems), and NEMS (nanoelectromechanical systems) are a combination of mechanical and optical elements, sensors, actuators, and electronic circuits on a structured substrate. Furthermore, MEMS and NEMS may contain optical, chemical, and/or biological components. To manufacture MEMS and NEMS, it is usually necessary to provide the surface of the structured substrate, in particular a wafer, preferably made of semiconductor materials and/or moldable plastics, with a coating. Photoresist is usually used for this purpose, in order to transfer lithographic structures in a further method step.
Coating microstructured and/or nanostructured structured substrates of this type has been shown to be difficult. In contrast to the semiconductor industry, where wafers having a comparatively even surface are used, the microstructured and/or nanostructured structured substrates of the MEMS/MOEMS and NEMS are comparatively thickly structured substrates. These deep structures are generated through wet or dry etching, embossing, or molding, and may have greatly varying shapes and greatly varying depths and flank formations. The structures of the structured substrate frequently have steep flanks and often even perpendicular side walls. Currently, it is typical that depressions implemented pits and/or holes having a depth of approximately 300 μm and a width or a diameter of the upper opening of approximately 100 μm and an angle of inclination of the side walls of up to 70° are lacquered uniformly. The methods known from the semiconductor industry for surface coating, such as spin lacquering, application of photoresist films, or immersion lacquering, are not suitable, since the coating substance may not penetrate up to the floor of the depressions. Currently, it is typical to coat the structured substrate in the spraying method. For this purpose, a fine coating substance mist is applied under standard atmospheric pressure to the surface of the structured substrate using an atomizer nozzle, the spray mist being deflected using air/oxygen or nitrogen (N2). The problem frequently arises in this case that the coating substance droplets close the narrow openings of the depressions because of surface tension and do not wet all of the side walls and the floor of the depressions. Furthermore, applying the spray mist through electrostatic charging, similarly to the powder coating method, to the structured substrate at standard pressure atmosphere is known. The high electrical voltage required in this case may destroy the sensitive structures and/or circuits of the structured substrate, however.